Bug 1835: Disable TLS 1.3 by default until it is better tested

https://winscp.net/tracker/1835

Source commit: b13e57c51fb80a001553f18f181fbb6c0062ddb5

source/core/SessionData.cpp

@@ -265,7 +265,7 @@ void __fastcall TSessionData::DefaultSettings()
   FtpTransferActiveImmediately = asAuto;
   Ftps = ftpsNone;
   MinTlsVersion = tls10;
-  MaxTlsVersion = tls13;
+  MaxTlsVersion = tls12;
   FtpListAll = asAuto;
   FtpHost = asAuto;
   FtpDeleteFromCwd = asAuto;